In recent years, with the rapid development of the construction industry, the amount of cement and concrete is increasing, and thus the cement admixture has become an essential important component in construction industry. The invention of polycarboxylate superplasticizer solved the problems of low water-reducing rate and slow setting for the first generation of lignosulfonate superplasticizer, and made up for the shortcomings of contaminated environment and fast slump loss for the naphthalene-based water reducer. Because of its advantages such as high water-reducing rate, good slump retention, fast strength growth and good compatibility, the polycarboxylate superplasticizer has become a research focus in the field of concrete admixture. As is known, the synthesis of polycarboxylate superplasticizer needs the important macromonomers namely polyoxyethylene ether and polyoxypropylene ether, which are mainly derived from ethylene oxide and propylene oxide. The industry production of polycarboxylate superplasticizer will be directly influenced once the supply shortage of ethylene oxide or propylene oxide occurs. Thus a new substitute material for the ethylene oxide and propylene oxide should be developed to get rid of the polycarboxylate superplasticizer industry's dependence on ethylene oxide and propylene oxide, which can enrich the synthetic methods of polycarboxylate superplasticizer.
With the development of design methods of molecular structure in the field of polymer science, the theoretical basis of synthesizing polymer with ideal molecular structure has been provided. The polycarboxylate superplasticizer designed and synthesized by us employs more affordable and more diverse raw materials, and possesses the comb-shaped structure similar to the structure of traditional polycarboxylate superplasticizer to ensure that it has a good anchoring force and stereo-hindrance effect. This polymer does not only possess several performances of traditional comb-shaped polycarboxylate superplasticizer, but also has some advantages including cheapness, independence of ethylene/propylene oxide and diversification of raw materials, manifesting as a very broad application value.
The patent CN1712381 (publication date: Dec. 28, 2005) reported a preparation method of polycarboxylate-g-polyether type concrete water reducer. This patent reported a method that the sulfonated styrene-maleic anhydride copolymer was obtained from sulfonating styrene-maleic anhydride copolymer by sulfonating agent without damage to anhydride groups, and then the sulfonated copolymer was mixed and reacted with polyethylene glycol followed by dissolving in water to obtain the polycarboxylate-g-polyether type concrete water reducer. This invention has the advantages of reasonable process, simple operation and mild reaction conditions. However, in this invention, the polyether was an important component of raw materials, showing a relatively simple variety of raw materials. The production of water reducer will be greatly influenced once the supply of raw material is limited.
The patent CN1288870 (publication date: Mar. 28, 2001) reported a preparation method of carboxylic acid graft type polycarboxylate superplasticizer. Two synthetic methods of carboxylic acid type polycarboxylate superplasticizer were provided in this patent. The one was that a polycarboxylate superplasticizer containing polyethoxylated side groups was copolymerized by the acrylate type monomers and the esterification product of polyoxyethylene and maleic anhydride. The other one was that a copolymer containing multi-functional groups such as carboxyl, hydroxyl and sulfonic groups was polymerized by unsaturated vinyl monomers containing side groups in a redox system. This invention method has the advantages of good product performance, easily obtained raw materials and good industrial prospects. However, in the first method of this invention, the polyoxyethylene of raw materials is also restricted by the supply of ethylene oxide; besides in the second method of this invention, the synthesized polycarboxylate superplasticizer with short side chains exhibits poorer stereo-hindrance effect than the conventional polycarboxylate superplasticizer with long side chains, showing a poorer dispersing effect to cement particles.
The patent CN103483504A (publication date: Jan. 1, 2014) reported a preparation method of the polycarboxylate superplasticizer synthesized by a macromonomer combination of two polyethers with different structures. In this patent, the isobutenyl polyethylene glycol, isopentenyl polyethylene glycol and water were added to the reactor, and then mixed and dissolved with stirring at 40-60° C., followed by adding acrylic acid and mercaptoacetic acid. After heated to 75-85° C., the aqueous solution of ammonium persulfate was dropwise added to the reaction system within 70-90 minutes followed by polymerization reaction for 2-3 hours at constant temperature. The polycarboxylate superplasticizer was finally obtained through cooling the resultants to room temperature and then adjusting the pH value to 6.8-7.2 by the aqueous solution of sodium hydroxide with a mass concentration of 30%. This polycarboxylate superplasticizer disclosed in the invention was synthesized by a copolymerization of macromonomer combination, which was beneficial to the balance between water-reducing and slump retention and the performance adjustment for the existing polycarboxylate superplasticizer products. However, in this invention, the polyether as one important component of raw materials is also restricted by the supply of ethylene/propylene oxide, which will influence the production and application of the products.
The polycarboxylate superplasticizer disclosed in the above patents mostly possesses good workability such as fluidity and dispersing ability. However, there are several shortcomings for all of the above preparation methods. All of the macromonomers used for synthesizing polycarboxylate superplasticizer are obtained from ethylene oxide or propylene oxide, manifesting as a relatively simple variety of raw materials. Once the ethylene oxide or propylene oxide is out of supply, the current production of polycarboxylate superplasticizer will be greatly influenced to further involve the concrete industry, leading to an inestimable loss. Hence, it is required that the substitutes for ethylene oxide and propylene oxide should be found as soon as possible to enrich the diversification of raw materials. Besides, it should play the similar role and mechanism in concrete system to achieve the excellent performances and ensure a high-efficient process operation and low preparation cost to industrialize easily. The related research in this area has not been reported in domestic and abroad.